Optical fiber networks lie at the core of modern telecommunication systems and infrastructures. As such, the development of reliable and accurate techniques for optical fiber characterization, inspection and testing is required to ensure network integrity and efficient signal transmission. Non-limiting examples of traditional fiber tests include optical fiber endface inspection, optical power level measurements, insertion loss and optical return loss testing, polarity determination, continuity verification, reflectance measurements, and the like.
Multi-fiber cables are commonly employed in premises optical fiber cabling, such as in data centers and other intrabuilding optical fiber networks that require high connectivity density and versatile solutions. Multi-fiber cables are mostly interconnected and connected to optical network equipment using MPO/MTP® connectors (MPO being the acronym for Multi-Fiber Push-On/Pull-Off connectors and MTP a brand name). The most common MPO/MTP® connectors are configured in a 1×12 fiber array, although 2×12, 2×16, and other fiber array configurations are also possible.
Preserving the cleanliness and quality of optical fiber endfaces forming part of multi-fiber connectors (MFC) is important for ensuring adequate network performance and maintain signal integrity. Video fiber inspection probes are commonly employed for inspecting and analyzing connectors, especially for hard-to-reach MFCs located on patch panels and bulkhead adapters. These probes are generally equipped with an optical source for illuminating the connector surface, a detector array for acquiring digital images of the connector surface, and a set of interchangeable adapter tips designed for most MFCs available on the market. The inspection results can be displayed on a suitable display unit.
Depending on the application, multi-fiber cables can be arranged in duplex or parallel configurations. In a duplex configuration, the fibers are arranged on MFCs such that each pair of adjacent fibers includes one transmitting fiber and one receiving fiber. In a parallel configuration, the transmitting fibers and the receiving fibers are physically separated into two groups of adjacent fibers on MFCs. The arrangement of receiving and transmitting fibers at an MFC defines what is referred to in the industry as the “fiber polarity” or, simply, “polarity”. System connectivity requires specific combinations of duplex patch cords, multi-fiber cables and optical fiber transition modules to properly manage polarities in duplex and parallel configurations. The TIA/EIA-568-C.3 Standard defines guidelines for maintaining fiber polarity and ensuring proper continuity between transmitters and receivers.
Since various multi-fiber array configurations are possible (e.g., duplex configuration, one-plug parallel configuration, two-plug one-row parallel configuration and one-plug two-row configuration), the TIA/EIA-568-C.3 Standard defines various types of multi-fiber cables, including Type A, Type B and Type C for 1×12 multi-fiber arrangements. Type A cables are designed with a key inversion but no duplex pair twists between the end connectors. Type B cables are designed with no key inversion and no duplex pair twists. Type C cables are designed with a key inversion and with duplex pair twists. Depending on the multi-fiber array configuration, various combinations of cable types may be required or desirable. Deployment mistakes can therefore easily occur if the intended cable type arrangement is not followed (e.g., due to human error or improper labeling), therefore causing improper polarity at the multi-fiber array connections.
Characterization of multi-fiber cable links aims to ensure and maintain network performance and integrity. Tier 1 characterization can include insertion loss and cable length measurements, polarity testing for fiber arrangement and/or cable type determination, and continuity verification. These tests can be performed with an optical loss test set (OLTS), typically including an optical source at one end of the cable link under test and an optical power meter at the opposite end. While OLTS-based methods for polarity testing may have certain advantages, they also have some drawbacks and limitations, notably in terms of cost.
Based on the foregoing, challenges remain in the field of multi-fiber cable testing.